Extragastrointestinal Stromal Tumor Of The Greater Omentum Presenting A Large Multilocular Cystic Mass: A Case Report And Review Of Literature

摘要

Primary neoplasms of the greater omentum are rare and and may pose difficulty for the preoperative histologic diagnosis. We report a case of extragastrointestinal stromal tumor of the greater omentum in a patient with chronic pancreatitis, which has been tentatively diagnosed of a benign omental cyst preoperatively. Computed Tomography showed a multiloculated large cystic mass of the greater omentum with multiple thick septa and a solid component and pancreatic calcification. Fine needle aspiration cytology showed a few histiocyte in a bloody background and it was negative for malignant cells. The patient underwent resection of the huge cyst including a major part of the greater omentum. Histologically, the tumor was consisted of sheets and strands of relatively uniform medium sized round epithelioid cells. Immunohistochemical staining of the tumor cells was positive for CD117 (c-kit, a transmembrane tyrosine kinase receptor), CD34 and vimentin, but it was negative for S-100 and Calretinin. These findings were compatible with extragastrointestinal stromal tumor (EGIST). We emphasized the possibility of extragastrointestinal stromal tumor of the greater omentum, although the preoperative radiologic findings suggested as a benign omental cyst. Introduction Extragastrointestinal stromal tumor (EGIST) is a unique tumor that occurs outside the gastrointestinal tract. EGIST shows c-kit expression and a histologic appearance similar to gastrointestinal stromal tumor (GIST)(1). Only a few cases of extragastrointestinal stromal tumor involving the mesentry, retroperitoneum and the bladder have been reported (1,2,3). In previous reported cases, most extragastrointestinal stromal tumors presented as a circumscribed or lobulated firm mass, and only rarely were cystic changes(1). In this paper, we describe a case of the extragastrointestinal stromal tumor of greater omentum that presented with a huge cystic mass. Case Report A 49-year-old man presented with abdominal distension and a palpable mass in his abdomen. He had history of alcoholic pancreatitis. Computed Tomography showed a multiseptated large cyst of the greater omentum and pancreatic calcification (Fig1).